Wood composites such as plywood are used in many indoor applications, in furniture and often in flooring applications. A major advantage of plywood over solid wood is that plywood does not warp, cup or twist, and does not swell or “move” as much as solid wood. However, there are many limitations to using plywood. The veneer used to cover the individual plys is often very thin, and prone to delamination. The coatings must also be sufficient to protect the thin veneer from scratching, because a scratch that goes through the thin veneer shows through to the underlying, less desirable inner plys. Also, water may cause swelling and buckling in plywood, as well as cracking. Thin veneer composite wood products of the prior art often have a coated surface that cracks due to the instability of the wood composite.
Polyethylene glycol (PEG) has a high molecular weight and is not very volatile. PEG has been used to treat wood by replacing the water with PEG, so that the passage of water in and out of the wood is no longer possible. The wood is typically heated in a vat containing PEG for an extended period of time to remove substantially all of the water and replace it with PEG. This type of process is not typically performed on veneer. Rather, these methods are used to stabilize ‘green’ wood and rely on materials such as polyethylene glycol to enter the cell walls of the ‘green’ wood and improve dimensional stability. These methods have been previously published. See “New and Better Ways to Dimensionally Stabilize Wood”, A J. Stam, Forest Products Journal, 9(1959):3, 107-110, and “Woodworker Heart,” Harry C. Leslie, Man Society Technology, A Journal of Industrial Arts Education, 33(1):13-16, September, October, 1973. A limitation of these processes is that they tend to rely on long soak times that are not typically practical for commercial production.
Veneer and planks have been impregnated with PEG and methylmethacrylate using a vacuum process to harden the veneer and planks. This batch process yields a product in which the concentration of PEG and methylmethacrylate is substantially uniform throughout the veneer and plank.
It would be advantageous to have a continuous method for treating veneer and planks using conventional coating apparatus, such that the treated veneer and planks, and resulting coated wood composite, are not prone to cracking. Further, it would be advantageous to have such a method, which minimizes the amount of treating material necessary to deter wood checking. The present invention provides such a method, and the corresponding treated wood composite.